This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-101335, filed Mar. 30, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a disk drive capable of at least reading data, using a head, and more particularly to a method and apparatus that are employed in the disk drive and suitable for retracting a head to a predetermined retract position when power supply has been interrupted.
2. Description of the Related Art
Hard disk drives (magnetic disk drives) for reading/writing data using a head are known as disk drives for at least reading data, using a head. Among the disk drives, those in which a ramp load system is installed have recently come to be available. In the ramp load system, when the apparatus is shifted to an idle state, the front end of an actuator, which supports a head, is retracted to a retract area, a xe2x80x9cramp, provided at the radially outermost side of a disk (disk medium). In other words, the head is moved to a position off the disk. Further, in a ramp load system, when the idle state is released, the head is moved from the retract area onto the disk, i.e. is loaded onto the disk. Suppose here that the idle state indicates both a state in which the disk has stopped rotating, and a state in which the supply of power to a part of a circuit is stopped while the disk is rotating.
In the ramp load system, since the head""s retract area is off the disk, the attachment of the head to the disk can be avoided when the disk does not rotate. Accordingly, the ramp load system is effective when increasing the recording density of the disk by smoothing the surface of the disk and reducing the floating amount of the head.
However, if unintentional power-off occurs while the head is floating on the disk in accordance with the rotation of the disk, it is very possible that the head will land on the disk and stick thereto. In light of this, in hard disk drives that employ a ramp load system, various types of contrivances have been made to automatically retract the head upon power supply interruption.
Jpn. Pat. Appln. KOKAI Publication No. 11-297014 discloses a method for retracting a head when the interruption of power supply has occurred. In this method, power supplied to a voice coil motor (VCM) driver is classified into three levels, those being supplied in different time periods. Further, in this method, at a first step, an actuator is stopped, then at a second step, a head is moved at a low speed to a position near a ramp, and at a third step, the head is accelerated and retracted to a retract position. This configuration enables the speed of the head at the time of its collision against the ramp to be set at a sufficiently low value, thereby reducing the damage to the ramp. At the aforementioned first to third steps after power supply failure, charges (electric energy), accumulated in capacitors c3, c1 and c2 while power is being supplied to the HDD, are supplied to the VCM driver. The capacitors are set such that a higher voltage is obtained from the capacitor c2 than from the capacitor c1.
The above-mentioned publication also describes that, instead of using the capacitors, the back EMF (electromotive force) of a spindle motor for rotating the disk is rectified and used as power to be supplied to the VCM driver at each step after power off. The back EMF of the spindle motor is generated due to its own inertia after power off.
The above-described prior art considers solving the problem of the ramp being damaged, upon a power supply failure, when that the head collides with the ramp at high speed when retracted. However, no consideration is given to solving the problem that, upon power supply interruption, the disk stops rotating, the floating amount of the head reduces and the head may stick thereto. Specifically, in the prior art, the actuator presently operating is stopped at the first step. At this time, since the supply of power has already stopped, the rotational speed of the spindle motor is further reduced while the actuator is being stopped. Accordingly, it is very possible that the spindle motor may stop rotating before the head is completely retracted, and hence the head may land and stick to the disk.
Moreover, in the case of small hard disk drives such as 1.8-inch ones, it is difficult for the charges accumulated in the capacitors or the back EMF of the spindle motor, to cover the power required by the VCM driver to retract the head upon power supply interruption, for the following reason: To cover the power, required to retract the head at the interruption of power supply, by only the charges of the capacitors, the capacitors must have a large capacitance. This makes it difficult to downsize the entire apparatus. In light of this, the use of capacitors is not suitable. On the other hand, in small hard disk drives, the spindle motor is also small and hence does not provide a high back EMF. Accordingly, it is difficult for only the back EMF of the spindle motor to cover the power required by the VCM driver to retract the head upon power supply interruption. Therefore, the use of the back EMF of the spindle motor is not suitable, either.
The present invention has been developed in light of the above circumstances, and aims to enable a reliable and safe retract of a head upon power supply interruption, without using capacitors of a large capacitance, even if the back EMF of a spindle motor is insufficient.
According to an aspect of the invention, there is provided a method of supplying, upon power-off of a power supply for a disk drive, a current to a voice coil motor to drive a head actuator that supports a head, thereby retracting the head onto a ramp provided outside a disk medium near an outer periphery of the disk medium. In the method, during the operation of the disk drive, a time period required to move the head from a position of the head to a predetermined retract change position, using a back EMF that occurs, upon the power-off of the power supply, in a spindle motor is determined to be a retract time period. Upon the power-off of the power supply, the supply of the back EMF of the spindle motor to the voice coil motor as a driving source for a head actuator is started. When the retract time period has elapsed after the power-off of the power supply, i.e. when the head has reached a position near the retract change position, the current to be supplied to the voice coil motor is switched from a current generated by the back EMF of the spindle motor, to a current generated by discharge of a retract capacitor that accumulates a charge from the power supply.
In the above method, the retraction of the head upon power supply interruption is realized in two stages, i.e. a first retract and a second retract. In the first retract, the head is moved to a position near the predetermined retract change position, using the back EMF of the spindle motor. In the second retract, the head is moved to the ramp using a charge accumulated in the retract capacitor.
Thus, upon power supply interruption, the current generated by the back EMF of the spindle motor and the charge accumulated in the retract capacitor are selectively used as a current source for the voice coil motor used to retract the head onto the ramp. In a hard disk drive of, for example, 1.8-inch type, even if the head cannot be retracted onto the ramp only using the back EMF of the spindle motor, the above configuration enables the retraction of the head onto the ramp without a large-capacitance capacitor.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.